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M. M. Hanson (University of Cincinnati)
New optical MK classification spectra have been obtained for 14 OB star candidates identified by Comerón et al.\ (2002 A&A, 389, 874) and presumed to be possible members of the Cyg OB2 cluster as recently described by Knödlseder (2000 A&A, 360, 539). All 14 candidate OB stars observed are indeed early-type stars, strongly suggesting the remaining 31 candidates by Comerón et al.\ are also early-type stars. However, of these 14 new OB stars, as many as half appear to be older (in a more evolved evolutionary state) than the previously studied optical cluster, making their membership in Cyg OB2 doubtful. So while some of the newly identified OB stars may represent a more extended halo of the Cyg OB2 cluster, the survey of Comerón et al.\ also picked up a larger fraction of non-members. Presently, estimates of the very high mass of this cluster (total M \approx 104 M\odot and over 100 O stars) first made by Knödlseder remain higher than our study can support. Despite this, the recognition of Cyg OB2 being a more massive and extensive star cluster than previously realized using 2MASS images, along with the recently recognized super star cluster Westerlund~1 only a few kpc away (Clark & Negueruela 2002 A&A, 396, L25), reminds us that we are woefully under-informed about the massive star cluster population in our Galaxy. Radio surveys may not be detecting these massive clusters if they are more than a few million years old. Our best hope for remedying this shortfall is through deep infrared searches and follow up near-infrared spectroscopic observations, as was used to identify candidate members of the Cyg OB2 association. This program is supported by NSF grant AST-9973922 to the University of Cincinnati.
The author(s) of this abstract have provided an email address for comments about the abstract: hanson@physics.uc.edu
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.